1. Field of the Invention
The invention relates to an image forming apparatus provided with image forming means, recording material supplying means having a plurality of recording material stacking portions, and fixing means having a heat member, and adapted to form an image on a recording material from the recording material supplying means by the image forming means, and fix the image by the application of heat by the fixing means.
2. Description of Related Art
There are known various image forming apparatuses, and above all, electrophotographic type image forming apparatuses spread widely. The electrophotographic type image forming apparatuses include a copying machine, a printer (such as an analog or digital printer using a laser beam or an LED), a facsimile apparatus, a word processor, etc., and each of these is usually provided with image forming means, recording material supplying means having a plurality of recording material stacking portions, and fixing means having a heat member.
As the heat member of the fixing means, use is generally made of a fixing roller heated by a heater, and a recording material is passed between the fixing roller and a pressure roller disposed in opposed relationship therewith, and a toner image on the recording material is fixed by the application of heat to thereby form a permanent image. When the recording material passes while being in contact with the fixing roller, the contact portion (passing portion) thereof has its heat taken by the recording material and therefore the surface temperature thereof lowers. For this reason, heater control is effected so as to maintain the surface temperature of the fixing roller at a value suited for fixing.
However, when the surface temperature of the recording material passing portion of the fixing roller is detected and the fixing roller is maintained at a temperature suited for fixing, the end portions of the fixing roller the recording material does not pass have their heat not taken by the recording material and therefore, the surface temperature of the end portions rises above the temperature suited for fixing, and temperature unevenness occurs between the central portion and end portions of the fixing roller. This temperature unevenness becomes greater when recording materials are continuously passed, and this leads to the problem that the end portions become high in temperature and these portions and the portions around them are heat-damaged. There also arises the problem that the non-passing portions are excessively heated and therefore electrical energy is uselessly consumed.